Abstract

Canada has a large number of high-rise buildings; according to the National Fire Protection Association (NFPA) 101 Life Safety Code, a high-rise building is defined as a building with the height of more than 23 meters or that is roughly 7 stories tall. Fires in high-rise buildings are often disastrous and cause huge losses if the buildings are not well protected against fires. Historically, a high-rise fire is more likely to happen in the lower floors according to the statistics. Driven by stack effect, the resulting smoke from fires may spread to the higher levels more easily via the vertical shafts, e.g. stairs, elevators, light wells, ventilation ducts, than through leakage openings in the building structure. It was reported that smoke spread through shafts counts for about 95% or more of the upward movement of smoke in typical high-rise buildings. Therefore, much attention has been paid to the study of the smoke movement in vertical shafts.

Analytical models, numerical simulations and experimental studies are the commonly used methods to study the smoke movement through building shafts. For simplification, most of the previous studies on the analytical models and numerical simulations assumed adiabatic shaft walls and did not take heat transfer between smoke and shaft boundaries into consideration. In fact, the smoke temperature strongly depends on the heat exchange with the shaft walls and may vary significantly depending on the height. An accurate estimation of the temperature profile in a shaft is crucial for the prediction of smoke movement during a fire, because the amount of smoke spreading through a shaft is closely coupled with the heat transfer during a fire. Numerical approaches normally include CFD model, zone model and mutizone network model, in which the mutizone network model is often used to study smoke movement during fires in high-rise buildings but temperature in each zone has to be specified by users due to the lack of energy model, which may results in errors in stimulation. In addition, full size experiments are often costly and unpractical to conduct, especially for high-rise buildings. Sub-scale experiment is the often used one but it lacks sound scaling law to maintain the similarity of scaled and full-size high-rise models.

The main objective of this research is to develop an analytical model and a numerical modeling approach of coupled heat and mass transfer of fire smoke movement through vertical shafts of high-rise buildings. Based on the analytical model, simple calculation method and empirical equation of neutral plane level were developed and validated by experimental data from the literature. It was found that the empirical equation is more accurate than the existing equation of neutral plane level. Studies on the dimensionless analytical solutions and similarity study were also conducted using the analytical model, which provide a new scaling method to sub-scale smoke spreads in high-rise shafts. The new scaling method was verified by experiments on different size and material shafts. The results indicated that compared to the common used scaling method, Froude modeling method, the new scaling method could achieve closer results between sub-scaled models and the full-size model. The numerical approach is based on a multizone program with an added energy equation, CONTAM97R, which can calculate the coupled heat and mass transfer inside the high-rise shafts. Different from floor zoning strategy (FZS) that is frequently used, a new zoning strategy called adaptive zoning strategy (AZS) was suggested by adapting the temperature gradient inside the shaft. Using this zoning strategy, a modeling method of smoke movement in shafts during high-rise fires by the mutilizone and energy network program was proposed. It was concluded that AZS could achieve similar accuracy results as FZS but with fewer zones.